With advancement of the semiconductor manufacturing processes, requirements on the integration level of modern electronic systems become increasingly higher, and correspondingly, miniaturization of components has become a problem of great concern in the whole industry. However, unlike integrated circuit (IC) chips that advance following the Moore's Law, radio frequency (RF) modules which are known as another kind of important components in the electronic systems are very difficult to be miniaturized. An RF module mainly includes a mixer, a power amplifier, a filter, an RF signal transmission component, a matching network and an antenna as key components thereof. The antenna acts as a transmitting unit and a receiving unit for RF signals, and the operation performances thereof have a direct influence on the operation performance of the overall electronic system. However, some important indicators of the antenna such as the size, the bandwidth and the gain are restricted by the basic physical principles (e.g., the gain limit under the limitation of a fixed size, and the bandwidth limit). The limits of these indicators make miniaturization of the antenna much more difficult than miniaturization of other components; and furthermore, due to complexity of analysis of the electromagnetic field of the RF component, even approximately reaching these limits represents a great technical challenge.
Meanwhile, as the modern electronic systems become more and more complex, the multi-mode services become increasingly important in wireless communication systems, wireless accessing systems, satellite communication systems, wireless data network systems and the like. The demands for multi-mode services further increase the complexity of the design of miniaturized multi-mode antennae. In addition to the technical challenge presented by miniaturization, multi-mode impedance matching of the antennae has also become a technical bottleneck for the antenna technologies. On the other hand, the rapid development of multiple input and multiple output (MIMO) systems in fields of wireless communications and wireless data services further heightens the requirement on miniaturization of antennae and, meanwhile, requires availability of a desirable isolation degree, desirable radiation performances and desirable interference immunity. However, the communication antennae of conventional terminals are designed primarily on the basis of the electric monopole or dipole radiating principles, an example of which is the most common planar inverted F antenna (PIFA). For a conventional antenna, the radiating operation frequency thereof is positively correlated with the size of the antenna directly, and the bandwidth is positively correlated with the area of the antenna, so the antenna usually has to be designed to have a physical length of a half wavelength. Besides, in some more complex electronic systems, the antenna needs to operate in a multi-mode condition, and this requires use of an additional impedance matching network design at the upstream of the infeed antenna. However, the additional impedance matching network adds to the complexity in design of the feeder line of the electronic systems and increases the area of the RF system and, meanwhile, the impedance matching network also leads to a considerable energy loss. This makes it difficult to satisfy the requirement of a low power consumption in the design of the electronic systems. Especially, for indoor directional antenna designs, the antenna gain cannot well satisfy the user's needs, and the directionality is not so good.